There are two main types of Edwards' syndrome.
Approximately 94% of babies with Edwards' syndrome will have the full form, where every cell in their body has three copies of chromosome 18, instead of two. Most babies with this form will die before infancy.
About 5% of babies with Edwards' syndrome will have the extra copy of chromosome 18 in only some of their body cells. This less severe form of the disease is known as mosaic Trisomy 18.
The severity of mosaic Trisomy 18 depends on the type and number of cells that have the extra chromosome. Some babies may only be mildly affected, while some can be severely disabled.
Around seven in every 10 babies born with mosaic trisomy will live for at least a year and, in rare cases, babies with the condition may survive into early adulthood.